Such a method is used particularly for manufacturing parts in thermostructural composite materials, e.g. materials capable of constituting structural elements and of retaining their mechanical properties at high temperatures.
Examples of thermostructural composite materials are the carbon-carbon (C--C) type composites and the ceramic matrix type composites (CMC).
In a C--C type composite, the reinforcement texture is in carbon fibers and is densified by carbon, while in a CMC-type composite, the reinforcement texture is in refractory fibers (carbon or ceramic fibers) and is densified by a ceramic matrix.
When the thermostructural composite material parts are produced by chemical vapor infiltration of the material constituting the matrix, through the accessible porosity of the reinforcement texture, the shape of said texture is generally maintained by means of a tool, normally in graphite. This tool makes it possible to confer to the fibrous reinforcement texture a shape approaching that of the part to be produced, and to compact said texture in order to obtain the required fiber density.
The fibrous texture held in the tool, is placed inside an oven in order to undergo a chemical vapor infiltration at temperatures which are kept relatively high.
The beginning of densification consolidates the texture by bonding the fibers together. The texture then has sufficient cohesion to retain its shape and to be handled, after being released from the tool, in order to continue the infiltration without the tool.
Initially, the material constituting the matrix tends to deposit on the surface rather than to penetrate to the core of the texture, resulting in a partial obturation of the surface porosity in those areas of the texture exposed to the gas flowing through the apertures of the tool. The result is that, after consolidation, a machining operation is often required in order to scale the texture, e.g. in order to remove the surface parts where the constituent material of the matrix has accumulated in too great quantity, and in order to make the porosity to the core accessible again.
Use of the tool involves disadvantages.
A tool in graphite is expensive to produce, particularly because of the machining that it requires, on the one hand to obtain the required shape, and on the other hand, to provide apertures giving to the gases used for infiltrating the matrix access to the texture to be densified.
Also, due to their bulkiness and their weight, the tools occupy a rather important part of the serviceable volume of the oven and they present high thermal inertia.
Moreover, the tool partly conceals the surface of the fibrous texture, which causes a densification which is not exactly uniform and a surface condition which is non-homogeneous and uneven.